1. Field of the Invention
The present invention relates to improved apparatus for the operation of cargo container handling cranes having a horizontal gantry supported at an elevated location above the cargo container pickup and deposition areas. More particularly, the present invention relates to the apparatus for reducing cargo container handling and transfer cycle times by employing positive residual sway arrest in a cargo container handling crane which transports containers horizontally along the gantry of the crane. Residual sway in the container pickup apparatus during lowering is arrested by passing it through a guide chute near the end of the lowering cycle.
2. Description of the Prior Art
The handling and protection of cargo or material during its transportation has been greatly facilitated by the advent of containerization many years ago. Rail mounted dockside gantry cranes having retractable booms have now been long accepted as the standard in the industry for loading and unloading containerized cargo and fungible bulk materials. The containers are moved by the cranes between waterborne vessels and dockside transportation equipment.
When a cargo container transport ship is berthed alongside a dock, a gantry crane is moved along the dock parallel to the ship to a position where a retractable boom can be extended across the beam of the ship above the ship's cells which are the cargo container carrying area. The retractable boom in its operating position extends horizontally outboard from the crane's superstructure and, in its retracted position, clears the superstructure of any ship berthed alongside the dock adjacent to the crane. Containers can be transported along the gantry of the crane between the dockside pickup and deposition area and any storage position located within the beam of a berthed ship in its holds or on its deck.
The gantry portion of the cargo container handling crane includes the retractable boom and a dockside portion and a rear extension of said boom supported by the crane superstructure. Trolleys run along the gantry and suspend cargo container lifting spreaders from fleet-through wire rope reeving for attaching to and picking up cargo containers. The purpose of a gantry crane is to move cargo containers a specific horizontal distance from a pickup area to a deposition area. In each operation, in the most usual situation, the pickup area is either a dockside location where a container is picked off of a flatbed trailer or transport truck or railroad car, and moved outboard by the crane and lowered into a shipboard cargo container cell, or the reverse, wherein a container is lifted from a cell onboard ship and moved to a dockside storage area or a truck, trailer or railroad car.
In a transfer cycle by a crane, the container must first be picked up, then lifted vertically, moved horizontally, and then lowered to its deposition area. During a portion of the move, vertical and horizontal movement of the container can occur simultaneously. For each transfer cycle, the crane must raise or lower a container a specific distance to clear the side of a ship, and a round trip transfer cycle takes a substantial period of time to handle one container. The container handling capacity of a crane is determined and limited by the transfer cycle time. It is an important consideration in the design of a crane to lower cycle times by any small improvement possible.
In addition to the portion of the transfer cycle time required to pickup, lift, move, lower, and deposit the container, there is also a delay at each end of the cycle because of sway or pendulum movement which is induced into the load by virtue of the starting and stopping of the horizontal movement of the container lifting apparatus along the gantry. It takes additional time to abate the sway and to position the container by selectively controlling the forward and reverse movement of the trolley.
Numerous methods and apparatus have been developed for arresting sway in containers and lifting spreaders suspended by wire rope reeving. The problem is most acute at the shoreside container pickup and deposition areas where the containers are picked up or deposited close to ground level from or onto truck or trailer beds, railroad cars, or stacks of containers, and where the lifting spreader is suspended at its longest pendulum length for this purpose.
Some of the methods and apparatus for arresting sway in suspended cargo containers are disclosed in the following patents: U.S. Pat. No. 3,375,938 for Anti-Sway Device; U.S. Pat. No. 3,532,324 for Antisway Mechanism; U.S. Pat. No. 3,739,922 for Sway-Arrest System Improvement; U.S. Pat. No. 3,825,128 for Sway-Arrest System; U.S. Pat. No. 3,945,504 for Anti-Sway System for a Spreader Suspended from a Crane; and U.S. Pat. No. 5,186,342 for Integrated Passive Sway Arrest System for Cargo Container Handling Cranes; all of which are assigned to the assignee of the present invention.
The problem of arresting sway in the cargo container lifting apparatus at the shipside end of the transfer cycle is abated somewhat due to the height of the ship's deck which shortens the length of the suspension ropes, reduces the effect of the pendulum motion, and allows the sway arresting apparatus to be more effective. The containers are lowered into cells in the holds of a ship and all of the cell guides extend upward to the ship's deck from within the holds of the ship. When the ship's cells are full and the containers are stacked and lashed on top of a ship's deck, the suspension ropes are shortened even further, reducing even more the effect of the pendulum motion and enhancing the effect of any sway arresting apparatus.
A more recent development in the field of cargo container handling which reduces even further the length of the suspension ropes at the shipside end of the transfer cycle is the development of the hatch coverless container ships but which unfortunately has increased the container transfer cycle time in the prior art gantry cranes. These ships were developed to reduce lashing work or container tie down time for containers stacked on the open deck of the ship. This development provides cell guides which project upwards from the deck of the ship and which therefore require every vertical movement of a container to clear not only the side of the ship but the tops of all the upward projecting cell guides as well which previously did not extend above the ship's deck. In every cycle, however, the shipside end of the transfer cycle deposits a container into the top of the decktop cell guides when the container suspension ropes are shortest and the effect of the pendulum motion is the least and the sway arresting apparatus of the prior art is most effective.
Despite the shipside cargo container sway arrest advantages, the container handling productivity for hatch coverless ships is considerably lower in comparison with conventional container ships. That is because the handling pass or transfer cycle is substantially longer due to the height every container must be lifted to clear the tops of the on-deck cell guides until stacked containers on a conventional ship's deck gradually increase the time of the handling pass or transfer cycle. In both conventional and hatch coverless ships, the most acute sway arrest problem occurs at the shoreside end of the transfer cycle, and there is no known prior art which deals with this problem apart from the methods and apparatus that are utilized to arrest sway in the same manner at either end of the transfer cycle.
A further improvement in the art of sway arrest at the shoreside end of a container transfer cycle is disclosed in the related invention for a Cargo Container Transfer System for Cranes wherein the lifting spreader is dropped through a guide chute at the shoreside end of the cycle before picking up or depositing a cargo container. The present invention is an improvement on the guide chute disclosed therein.
The improved guide chute of the present invention overcomes the limitations of the prior art sway arrest devices by providing more efficient double function apparatus and method of operation for sway arrest apparatus which lower the cycle transfer time by effectively arresting residual sway of cargo container lifting apparatus at the shoreside end of the transfer cycle.